1. Field of the Invention
The present invention pertains to a method of etching silicon oxynitride and other oxygen-containing materials. Silicon oxynitride is primarily used as an antireflective coating (ARC) and is often referred to as a "dielectric ARC". Silicon oxynitride is frequently used in combination with deep ultraviolet (DUV) photoresists.
2. Brief Description of the Background Art
In the field of semiconductor device fabrication, DUV photoresists have been developed which take advantage of shorter wavelengths of ultraviolet radiation to enable the patterning of smaller electronic and optical devices than possible with traditional, or so called I-line, photoresists. Generally, the photoresist is applied over a stack including layers of various materials to be patterned in subsequent processing steps. Some of the layers in the stack are consumed during the process of patterning underlying layers which become part of the functioning device. To take advantage of the spacial resolution of the photoresist, it is necessary to use an antireflective coating (ARC) layer underlying the photoresist in order to suppress reflection off other layers in the stack during photoresist exposure. Thus, the ARC layer enables patterning of the photoresist to provide an accurate pattern replication.
Though the most commonly used ARC material is titanium nitride, a number of other materials have been suggested for use in combination with DUV photoresists. For example, U.S. Pat. No. 5,441,914, issued Aug. 15, 1995 to Taft et al., describes the use of a silicon nitride antireflective layer, while U.S. Pat. No. 5,525,542, issued Jun. 11, 1996 to Maniar et al., discloses the use of an aluminum nitride antireflective layer. U.S. Pat. No. 5,539,249, issued Jul. 23, 1996 to Roman et al., describes the use of an antireflective layer of silicon-rich silicon nitride.
U.S. Pat. No. 5,635,338, issued Jun. 3, 1997 to Joshi et al., describes a class of silicon-containing materials which display particular sensitivity in the ultraviolet and deep ultraviolet for the formation of patterns by radiation-induced conversion into glassy compounds. Joshi et al. recommend the use of antireflective coatings such as amorphous silicon and an organic plasma polymerized antireflective coating generated from cycloheptatriene.
U.S. Pat. No. 5,633,210, issued May 27, 1997 to Yang et al., discloses the use of an antireflective coating material selected from titanium nitride materials, silicon oxide materials, and silicon oxynitride materials.
Recently, there has been increased interest in the use of silicon oxynitride as an antireflective coating due to its ability to function well in combination with DUV photoresist. Silicon oxynitride typically (but not by way of limitation) has a formula of SiO.sub.x N.sub.y H.sub.z, where x ranges from 0 to about 2, y ranges from 0 to about 1, and z ranges from 0 to about 1. By changing the composition of the silicon oxynitride ARC layer, one can control reflection onto the photoresist during imaging of the photoresist layer. When SiO.sub.x N.sub.y H.sub.z is used as an ARC, x, y, and z typically range between about 0.2 and about 0.5.
Silicon oxynitride as an ARC enables efficient suppression of the reflection from underlying layers, while providing superior chemical properties which prevent an undesirable effect, known as photoresist poisoning, in photoresist patterning. Photoresist poisoning refers to reaction of the surface underlying the photoresist with moisture to form amino basic groups (NH2.sup.-) which react with the photogenerated acid which is responsible for the photoresist development. Deactivation of the acid by the amino groups is believed to be responsible for formation of the "foot" (widening of the photoresist line just above the substrate) on some ARC materials, such as titanium nitride.
The present invention addresses details of the application of dry etch techniques for pattern transfer into a silicon oxynitride layer. However, the concepts developed for dry etch of a silicon oxynitride layer have application to the dry etch of other oxygen-containing substrates.
With reference to a silicon oxynitride layer used as an antireflective coating, in such an application, a typical stack of materials for pattern transfer would include (from bottom to top): A substrate, which is a dielectric layer used to separate a metal interconnect layer (to be patterned on plasma etching of the etch stack) from underlying layers of the integrated circuit; a barrier layer, which prevents the diffusion of material between a conductive layer and the substrate; a conductive layer, which is typically aluminum or an alloy thereof, an antireflective coating (ARC) layer, which reduces reflection back into the photoresist during its exposure in the lithography step and allows for better pattern reproduction; and, a photoresist layer, which is imaged to provide the pattern for transfer to underlying layers.
It would then be desirable to have a dry, plasma-based etch process for transfer of the pattern from the developed photoresist through all of the layers within the complete etch stack, including an ARC layer, a conductive layer, and a barrier layer. Etching of a metal-comprising stack is traditionally achieved in a metal etch chamber using etch stacks with ARC layers such as titanium nitride. However, as silicon oxynitride is a dielectric material, its patterning is traditionally reserved for dielectric etch chambers used for etching oxide and nitride. As a result, the substrate is typically moved from one process chamber to another, which lowers the overall productivity of the whole process.
The present invention details a method permitting the etch of a dielectric-comprising ARC layer, such as a silicon oxynitride ARC, in the same chamber as is used for etching the rest of the metal-comprising stack. We have developed a plasma etch process which provides adequate selectivity for etching a silicon oxynitride ARC layer over organic-based photoresists. In addition, we have obtained a good etch rate for a silicon oxynitride ARC layer, while providing excellent pattern transfer through the ARC layer and other layers of a six-layer, metal-comprising stack. Further, the method of the invention solves a series of integration problems stemming from the fact that the chemistry used for etching the silicon oxynitride ARC layer is very different from that used in the metal etch.